Targeted Pre-Treatment of Hemp Fibers and the Effect on Mechanical Properties of Polymer Composites

Abstract

Research on plant-fiber-reinforced composites has gained significant research interest since it generates composites with exceptional mechanical properties; however, the potential of hemp fibers can only be fully exploited if the fibers are well separated from the bundle to achieve cellulose-rich fibers. This is because well-separated bast fibers that are long and exhibit higher fiber aspect ratio enhance the mechanical properties of the composite by influencing property translations upon loading. A key feature for successful implementation of natural fibers is to selectively remove non-cellulosic components of hemp fiber to yield cellulose-rich fibers with minimal defects. Targeted pre-treatment techniques have been commonly used to address the aforementioned concerns by optimizing properties on the fiber’s surface. This in turn improves interfacial bonding between the fibers and the hydrophobic polymer, enhances the robustness of hemp fibers by improving their thermal stability and increases resistance to microbial degradation. In this study, we comprehensively review the targeted pre-treatment techniques of hemp fiber and the effect of hemp fiber as a reinforcement on the mechanical properties of polymeric composites.

The Influence of the Chemical Composition of Flax and Hemp Fibers on the Value of Surface Free Energy

“…The advantage of water retting is that it takes place in completely controlled conditions, which makes it superior to the dew-retting method [ 57 ]. It also allows obtaining higher quality fiber by removing non-cellulosic components for spinning applications.…”

“…Comparison of dew and water-retting methods and the quality of fibers obtained using these methods has been the subject of literature [ 57 , 58 , 59 , 60 , 61 , 62 ]. Dew retting is widely used due to its low impact on the environment and economic conditions, but the course of the retting process depends on weather conditions [ 62 ].…”

“…The retting process on the field is difficult to control and may result in a diversity of fiber quality. Water retting is a short-term process under controlled conditions [ 57 ], but due to heavily polluted sewage, retting cannot be used in countries in Europe and other countries [ 61 ].…”

“…A comparison of the chemical composition of hemp fibers extracted with the use of the applied retting methods showed that the fiber obtained by the water retting is characterized by a significantly lower lignin content compared to the fiber obtained by the dew retting. It was also shown that pectin content in water-retted fibers was lower in comparison to dew-retted hemp fibers showing that water retting removes pectin from the fiber more effectively than dew retting due to the fact that pectin is partially soluble in water [ 57 ]. The tests showed that the BIAŁOBRZESKIE fiber obtained in the water-retting process is characterized by lower waxes and fat content compared to the fiber obtained by the field dew-retting method.…”

From Hemp Waste to Bioactive Nanofiber Composites: Deep Eutectic Solvents and Electrospinning in Upcycling Endeavors

“…Nevertheless, these plant fibers are highly prone to wrinkling, display a hydrophilic character, and are susceptible to contamination and microbial attack. Hence, there is a need for approaches that can enhance their performance to microbial degradation [14]. Moreover, although hemp fibers have the potential to be used by different industries, hemp stumps are typically discarded as agro-waste [6,9].…”